Multiple axle suspension



P 1965 L. E. EISENHAUER ETAL 3,204,977

MULTIPLE AXLE SUSPENSION I Filed Jan. 8, 1962 8 Sheets-Sheet l N INVENTORS MWW A TTOAA EYS p 7, 1965 L. E. ElSENHAUER 'ETAL 3,204,977

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MULTIPLE AXLE SUSPENSION 8 Sheets-Sheet 8 Filed Jan. 8, 1962 INVENTORS lE/G/l ./SEIY/ffll/R m: l 5 BY Mm mm A T TOR/VEYS United States Patent 3,204,977 MULTIPLE AXL SUSPENSION Leigh E. Eisenhauer and Ancil C. Stover, Van Wert, Ohio, assignors to William A. Eisenhauer, William P. Ellwood, Ida J. Eisenhauer, and Leigh E. Eisenhauer, ctr-partners, doing business as The Eiseuhauer Manufacturing Company, Van Wert, Ohio Filed Jan. 8, 1962, Ser. No. 164,818 8 Claims. (Cl. 280'81) This invention relates to vehicles 'of the type having tandem axles supported for turning movement about generally vertical axes.

In vehicles of this type, two or more of the axles are pivotally supported on the frame so that when the vehicle is turned from a straight course of travel, the pivoted axles will turn in appropriate direct-ions to track with the front steering wheels. This action has the advantage of minimizing side and lateral skidding of the ground engaging wheels when a turn is negotiated, but has the disadvantage of decreasing stability.

In United States Patent 2,643,895 issued June 30, 1953, there is disclosed a hydraulic stabilizer system the function of which is to substantially parallel the action of the steering forces that cause the pivoted axles to track with the front steering wheels. Accordingly, the stabilizer system therein disclosed does not interfere with the natual tracking pattern, and at the same time it cancels out other forces tending to disturb the natural tracking pattern. One of the deflecting forces tending to disturb the natural steering pattern is centrifugal force. Another is that which results when uneven rolling resistance is met by either wheel of an axle. The function of a hydraulic stabilizer is to combine the forces represented by the natural steering functions of two axles making available suflicient force to maintain directional stability, as these conditions are met by the individual axles.

With the above in view, one object of this invention is to provide ahydraulic stabilizer system for the pivoted axles of a tandem axle vehicle which correlates the turning movements of the pivoted axles so that they track in a pattern which closely follows but is not precisely the same as the pattern which the axles theoretically tend to assume in response to natural steering forces.

More specifically, the hydraulic stabilizer of the present invention so correlates the turning movements of the pivoted axles as to cause the front axle to over-steer the natural or mean theoretical tracking pattern, and the rearrnost axle to under-steer. As a result, the vehicle will have greater stability and the rear axle will not hunt or fishtail. At the same time, tire wear is greatly reduced and wear on all tires will be more nearly equal.

Another object is to provide a vehicle suspension in which the road impacts sustained by individual axles are distributed over several axles and springs. In this way, vertical deflection of several springs and axles are combined to cushion or soak up impact forces received at any particular axles. This in turn will make it possible to reduce considerably the mean deflection range of the suspension, suiting it peculiarly for the employment of single leaf springs with their high rate, high frequency and inertia characteristics. Since lateral stability is affected by suspension rate and deflection range, a flatter, more stable ride will result without a corresponding sacrifice of ride quality.

Another object is to provide a suspension wherein the suspended load at a given axle will not increase appreciably as it is elevated.

Another object is to provide means for automatically locking pivoted axles against turning movement in respouse to the operation of the brakes or the reverse mechanism of the transmission.

Other objects and features of the invention will become apparent as the description proceeds, especially when taken in conjunction with the accompanying drawings, wherein:

FIGURE 1 is a top plan View of a three axle trailer constructed according to the invention.

FIGURE 2 is a view taken on the line 22 of FIG- URE 1.

FIGURE 3 is a view taken on the line 33 of FIG- URE 1.

FIGURE 4 is a view taken on the line 4-4 of FIG- URE 2.

FIGURE 5 is a view taken on the line 5.-5 of FIG- URE 3.

FIGURE 6 is an enlarged fragmentary sectional View of a portion of FIGURE 3, illustrating the pivotal support for one of the axles.

FIGURE 7 is a fragmentary top plan View illustrating a portion of the torque rod connection of an axle to the frame.

FIGURE 8 is a fragmentary top plan view illustrating the remainder of the torque rod connection between an axle and the frame. 7

FIGURE 9 is a view taken on the line 9-9 of FIG- URE 7.

FIGURE 10 is a view taken on the line 1010 of FIGURE 8.

FIGURE 11 is an enlarged fragmentary view, partly in section, showing the pivoted link connection between an end of a leaf spring and the adjacent end of a stabilizer bar.

FIGURE 12 is an enlarged View, partly in section, of the structure shown in FIGURE 11, as viewed from the right.

FIGURE 13 is an enlarged sectional view illustrating the connection between a leaf spring and one of the axles.

FIGURE 14 is a view partly in section illustrating the connection of the leaf spring and another axle.

FIGURE 15 is a diagrammatic view of the trailer showing the relative positions of the axles when a turn is negotiated.

FIGURE 16 is similar to FIGURE 15 but shows atwo-axle trailer.

FIGURE 17 is a combined hydraulic and electrical diagram.

Referring now more particularly to the drawings, the trailer chassis has a frame 10 comprising side sills 12, secured in laterally spaced relation by crossbars 14. Extending beneath the frame 10 in a direction transverse to the length of the frame are a plurality of axles desig nated by the numerals 16, 18 and 20. The axles are connected to the frame 10 by suspensions 19 and 21 on either side of the frame each including the elongated single leaf springs 22 and equalizer bars 24 and 26. Two springs are provided for each axle, respectively connected to the axle on either side of the frame and inside the ground engaging wheels 27. The springs 22 are mounted on the axles 16 and by spring mounts 30, and are mounted on the axle 18 by spring mount 32.

Referring to FIGURE 13, each spring mount has an upper oscillating seat 34 and a lower oscillating seat 36. A wear plate 37 lays on top of the upper seat 34 and is provided with a hole 38 adapted to align with the hole 40 in the upper seat 34. The spring 22 likewise has a hole, designated 42, adapted to register with the holes 38 and 40, and a pin 44 extends through the registering holes to properly align the parts. The spring is clamped down on the wear plate 37 of the upper seat by a clamp 46 and U-shaped bolts 48 extending over the top of the clamp and secured at their lower ends to bosses 50 on the upper seat 34 by nuts 52 threaded on the lower ends Patented Sept. 7, 1965 of the bolts. \Vhen nuts 52 are tightened, they draw the clamp 46 down tightly upon the spring 22, and the pilot pin 44 prevents the spring from moving laterally. As will be understood from an inspection of FIG. 2, the bolts 48 are clear of the upper seat 34 at either end thereof and hence do not interfere with its oscillating movement.

The lower seat 36 has a body 54 provided with an opening 56 which at the upper end is of reduced cross-section to provide the annular shoulder 58. A wear plate 60 secured to the upper surface of the body 54 has a central aperture registering with the reduced cross-section portion of the opening 56. A tubular bushing 62 extends through the reduced portion of the opening 56 in the lower seat, through the registering aperture in the wear plate 60 and into a recess 64 in the underside of the upper seat34, and a bolt 66 extends through the tubular bushing and threads into the upper seat. The head 68 of the bolt bears against the underside of the bushing to clamp it tightly to the upper seat. A disk-shaped bearing 70 is provided between the underside of the upper seat and the wear plate 60 of the lower seat, having an aperture to receive the tubular bushing 62. A disk-shaped bushing 72 is provided between the flange 74 on the lower end of the bushing and the shoulder 58, likewise apertured to clear the bushing 62. A tubular bearing 76 surrounds the bushing 62 within the aperture in the Wear plate60 and the reduced portion of the opening 56 in the lower seat. Extending beneath the body 54 of the lower seat are the laterally spaced legs 7 8, and a pin 80 extends between the legs encircled by the tubular portion 82 of a bracket 84 rigidly secured to the axle 16 or 20. A tubular bearing 86 is disposed between the portion 82 of the bracket and pin 80. v The connection between the axle 16 or the axle 2t) and either spring 22 provided by the spring mounts 30 is such that the spring can rotate with respect to the axle about the vertical axis of the bolt 66, by' reason of the fact that the spring is connected to the upper seat 34 and the axle is connected to the lower seat 36, the seats themselves being rotatable with respect to each other about the bolt. The lower seat can also pivot relative to the axle about the horizontal'axis of the pin 80 which is parallel to the axle. The spring mounts 32 for connecting the springs 22 to the middle axle 18 are of a somewhat different construction. As illustrated in FIGURE 14, the spring mount 32 has a main body portion 87, and the spring 22 is clamped down on the top surface thereof by a clamp 88. A pilot pin 90 extends into registering holes in the spring and in the body 87 to prevent relative shifting movement. The clamp 88 is drawn down tightly upon the spring 22 by the U-shaped bolts 92 which extend through openings in the upper portion of the body 87 andhave nuts 94 threaded on the lower ends thereof. The body 87 is formed with the laterally spaced legs 96, and a pin 98 extends between the legs. A bracket 100 secured to the axle .18 has a tubular portion 102 encircling the pin 98, and a bearing 104 is disposed between the tubular portion and the pin.

The arrangement is such that the axle 18 can move with respect to the spring mount about the spring axis of the pin 98, which is parallel to the axle. The axle cannot move about a vertical axis with respect to the spring, but such movement is unnecessary in view of the fact that axle 18 is fixed with respect to the frame of the trailer against angular movement or movement about a vertical axis, as will become apparent as this description proceeds. Referring again to FIGURES 1 and 2, it will be noted that the springs 22 along one side of the trailer extend in alignment longitudinally thereof, as do the springs along the opposite side. Links 110 are provided for connecting the ends of the springs to the stabilizer bars 24 and 26 and to the brackets 112 and 114 rigidly carried by the frame 10. Each link 1111 has a generally U-shaped link body or arm 116 formed with a reduced cylindrical portion at either end providing parallel pins 118 and 119 which lie in vertical planes extending longitudinally of the trailer (FIGS. 11 and 12). A shackle 120 has a tubular portion 122 sleeved on the pin 118, and a bearing 124 is interposed between the pin and the tubular portion. The shackle 120 is retained on pin 118 by retainer 140 and bolt 142. The shackle 120 has legs 126 connected by a horizontal pivot pin 128. The spring 22 has an eye 130 at the end loosely encircling the bearing 132 sleeved on pin 128. The pin 128 is at right angles to the pins 118 and 1119 and to the longitudinal center line of the trailer.

The shackle 134 has a tubular portion 136 sleeved on the pin 119, and a bearing 138 is interposed between the pin and the tubular portion. The shackle 134 is retained on pin 119 by the retainer 140 and bolt 142. The shackle 134 has legs 144 connected by horizontal pivot pin 146. The equalizer bar 26 has a hole 148 encircling the pin 146, and a bearing 150 is provided between the hole and the pin. The pin 146 extends at right angles to the pins 1181 and 119 and to the longitudinal center line of the trai er.

While in FIGURES 11 and 12 the link 110 is shown connected to the end of the equalizer bar 26, it will be understood that others of the links are pivoted to the equalizer bar 24 and to one or the other of the brackets 112 and 114 on the trailer frame.

It will be understood that the suspensions 19 and 21 along either side of the trailer, composed of springs, spring mounts, equalizer bars and links, are exactly the same. The equalizer bars 24 are pivoted on aligned axes 158 to brackets 154 on the frame 10, and the equalizer bars 26 are pivoted on aligned axes to bracket 156 on the frame. The equalizer bars 24 and 26 are pivoted to the frame brackets at points midway between their pivotal connections with links 110.

' Axles 16 and 20 are connected to the vehicle frame for turning movement about vertical axes, while the axle 18 is connected to the frame in a manner such that it cannot turn nor shift laterally. Referring to FIGURES 3 and 6-10, the connection with the frame of the axle 20 will be described. As seen in FIGURE 6, a vertical tube 160 is rigidly secured to the frame 10 on the central longitudinal axis thereof, and a tube 162 of smaller diameter is supported coaxially within the outer tube for rotation with respect thereto. The outer tube is provided with the vertically spaced cone-shaped bearings 164, and the inner tube is provided with the vertically spaced coneshaped bearings 166 which respectively engage the bearings 164 to support the inner tube for rotation with respect to the outer tube while holding the tubes against relative axial movement. A horizontal cross-tube 168 is located forwardly of the tube 162 and is rigidly connected to the lower end thereof by the member 170.

Referring now to FIGURES 7 and 9, the tube 168 has the laterally spaced brackets 172 and 174 fixed thereto which respectively carry one end of torque rods 176 and 178. Torsillastic bearings 180 are provided to pivotally connect the ends of the rods 176 and 178 to the respective brackets 1'72 and 174. As shown, the bracket 174 has a cylindrical passage 182, andextending into the passage is a pin 184 rigid with the end of the torque rod 178. A rubber bearing 186 is provided in the space between the passage 182 and the pin 184, being bonded to the surfaces of each. Hence the torque rod 17 8 can rotate to a degree with respect to the bracket 174, but such rotation is resisted by the rubber bearing 186. The torsillastic hearing 180 connecting the end of rod 176 and bracket 172 is exactly the same, and the pins 184 of the bearings are in horizontal alignment with each other.

The axle 20 is provided with the laterally spaced brackets 188 and 190 rigidly secured thereto, and the opposite ends of the torque rods 176 and 178 are respec tively pivotally connected to the brackets 188 and 190 by torsillastic bearings 180. The pivots 184 of the torsil lastic bearings are of course rigidly carried by the ends of the torque rod and are horizontally aligned with each other.

Referring to FIGURES 8 and 10, it will be noted that the connect-ion between the cross-tube 168 and axle also includes a second pair of torque rods 194 and 196. The corresponding ends of these .torque rods are respectively pivotally connected to the brackets 198 and 200 rigidly secured to the cross-tube 168 in laterally spaced relation, by torsillastic bearings 180 which are of exactly the same construction as those already described. The pins 184 of the torsillastic bearings 180 are rigidly carried by the ends of the torque rods and are in horizontal alignment with each other. The opposite ends of the torque rods are pivotally connected to the brackets 202 and 204 rigidly carried by the axle 20 in laterally spaced relation, by torsillastic bearings 180. The pins 184 of these torsillastic bearings are rigidly secured to the ends of the torque rods and in horizontal alignment with each other.

The arrangement is such that the pins 184 of the torsillastic bearings are all parallel to the cross-tube 168 and to the axle 20. These axes extend horizontally, and it will be noted in FIGURE 3 that the pivots at the ends of the torque rods define a parallelogram. Hence the axle 20 can swing up and down in an arc as controlled by the torque rods.

The connection between the front axle 16 and the frame is exactly the same as that for the rear axle 20 except that the cross-tube 168 is connected directly to the lower end of the tube 162, rather than to an intermediate connecting member such as 170.

The connection of the middle axle 18 to the frame differs from the others in that the cross-tube 168 is con nected directly to the brackets 154 of the frame in alignment with the stabilizer bar pivots 158.

In accordance with this construction, the axles 16 and 20 can turn with respect to the vehicle frame but the middle axle is a fixed axle and hence cannot turn. All of the axles, however, can swing up and down in an are as controlled by the torque rods 176, 178, 194 and 196. It will be noted that the torque rods 176 and 178 are at an angle to each other Whereas the torque rods 194 and 196 are parallel. Specifically, when the axles are at right angles to the frame, the rods 176 and 178 are displaced equal distances from and on opposite sides of the longitudinal center line of the frame and converge toward one another at the same angle with respect to the center line. opposite sides of the longitudinal center line of the frame, they are also parallel to the center line. The purpose of providing an angular relationship between the torque rods 176 and 178 is to prevent the axle from shifting axially or in the direction of its length.

When the steerable axles 16 and 20 turn, the spring mounts move with them laterally with respect to the vehicle frame. This requires a lateral movement of the springs 22 connected thereto. Such movement of the springs 22 is permitted by the unique pivotal connection provided by the links 110. The springs 22 will remain substantially parallel to the center line of the frame without pivoting while they move laterally with respect to the vehicle frame during turning of the steerable axles 16 and 18, since the spring mounts 30 permit a relative turning movement between the axles and the springs.

It will be appreciated that when an individual axle is elevated above the mean suspension height, that is above the position illustrated in FIGURES 2 and 3, the variable rate characteristic of the torsillastic bearings 180 of the torque rods will progressively increase the suspended load at the axle as it is elevated. This is counteracted by the arrangement of springs, equalizer bars and links shown. For example, if the axle 20 is elevated above the mean suspension height, the springs 22 associated therewith will incline upwardly toward the left, and accordingly the equalizer bars 26 will incline upwardly toward the right.

While the torque rods 194 and 196 are on The increased tension in all of the links will cause the springs 22 of the axles 16 and 18 likewise to incline upwardly toward the left and the equalizer bar 24 to incline upwardly toward the right. Likewise the increased tension in the links 110 will tend to elevate the frame atthe points of pivotal connection 158 and 160 of the equalizer bars.

Accordingly, there is a progressive unloading of the elevated axle. Stated differently, as an axle is raised above the mean suspension height, a progressive leverage advantage will occur at that axle, thus countering the load ing effect of the torque rod bearings. Not only are road impacts thus distributed over several wheels and springs, but when weighing a vehicle one axle at a time as is ordinarily done (these scales are about six inches high), a more accurate reading will result.

Because of the distribution of road impacts at one axle over the several axles and springs, vertical deflections of the several springs and axles are combined to cushion or soak up impact forces as received at each wheel. This will in turn make it possible to reduce considerably themean deflection range of the suspension, suiting it peculiarly to the employment of single leaf springs with their high rate, high frequency, and low inertia characteristics. As suspension rate and deflection range are functions of lateral vehicle stability, a flatter, more stable ride will result without a corresponding sacrifice of ride quality.

Stability is further enhanced by the manner in which the spring ends are connected to the stabilizer bars. Con nected in the manner shown, the leaf springs will in effect tend to increase the stable load base from a width represented by the spring centers to the much wider track of the ground wheels. Then too, single leaf springs as herein employed further improve stability by their high rate under reverse deflection as compared with multi-leaf springs, which necessarily must depend on the main leaf only during reversal of load forces. In this connection, it might be noted that lateral thrust against the body of a vehicle (centrifugal force on a turn, side hill thrust, etc.), particularly in a high center of gravity load, can, if of suflicient magnitude, actually lift or pick up the load from the points of bearing on the spring tips on the thrust side of the vehicle.

The front and rear axles 16 and 20 are steerable axles, by reason of the caster effect provided by their pivotal connection with the frame. In other words, the axles 16 and 18 are displaced rearwardly from their pivotal connection to the frame and hence will tend to track or assume a natural steering pattern when the vehicle is turned from a straight course. With reference to FIGURE 15, the line 210 is drawn at right angles to the center line of a towing vehicle pivotally connected to the trailer at 212. When the towing vehicle is pulling the trailer at this angle, the line 210 will intersect line 214, which is an extension of the fixed axle 18', at the point 216. Point 216 may be considered the center of turning. Theoretically, the steerable axles 16 and 20 will turn in response to the steering forces and assume a 1 natural steering pattern in which their axles, or a projecttion thereof, will pass through the point 216. The pro jected axles when following a natural steering pattern wholly in response to steering forces are indicated by the lines 213 and 220. It will be understood of course that there are forces tending to disturb the natural steer-- ing pattern. One such is centrifugal force. Another re sults from uneven rolling resistance of the wheels of a given axle.

The stabilizer system shown in Patent 2,643,895 controls the steerable axles so that they will assume a natural steering pattern and so that deflecting forces tending to disturb the natural steering or tracking pattern will be cancelled out. However, it has been discovered there are advantages to a stabilizer which controls the steering movement of the pivoted axles so that they track ina pattern which is close to but departs somewhat from a natural steering pattern. In accordance with this invention, and with reference to FIGURES 1 and 17, there are pivoted to the vehicle frame 10 adjacent the two steerable axles 16 and the hydraulic cylinders 230 and 232 which are of identical size and construction. The pivots are indicated at 234. Pistons 235 are respectively slidably supported in the two cylinders, and their piston rods 236 and 238 are respectively pivotally connected at 240 to the arms 242 and 244 secured to the rotatable tubes 162 providing the pivotal support for the respective axles 16 and 20. With reference to FIGURE 17, it will be seen that the piston ends of the cylinders are connected by conduits 250 and 252 through an aspirating valve 254. The aspirating valve 254 permits a free flow of hydraulic fluid therethrough, and is provided to withdraw air from the conduits and return it to the hydraulic reservoir 256 via conduit 258. For a more complete description of a suitable aspirating valve, reference is made to Patent No. 2,761,693. It will also be noted in FIGURE 17 that the rod ends of the cylinders are connected together by conduits 260 and 262 through a similar aspirating valve 264 provided to bleed air from the lines and return the same to reservoir 256 via line 266.

Since the cylinders are the same size, it will be understood that a given displacement of the piston in one cylinder will result in the same displacement of the piston in the other cylinder by reason of the exchange of hydraulic fluid therein. However, the amount of turning of the respective axles varies in proportion to the lengths of the arms 242 and 244 connecting the piston rods to the respective tubes 162 which pivotally mount the axles.

It it were desired that the stabilizer constrain a movement of the steerable axles 16 and 20 such that they follow the natural steering pattern, then the ratio of the length of the arms 242 and 244 would be in inverse proportion to the distances from the fixed axle 18 (which is the center of suspension or support) to the axles with which such arms are associated. In other words, assuming the distance between axles 16 and 18 to be 49 inches and the distance between axles 18 and 20 to be 109 inches, then the ratio of the length of the arms 244 and 242 would be 49 divided by 109.

However, the present stabilizer is designed to cause the rear axle to under-steer and the front axle to oversteer. Preferably, the rear axle will under-steer the mean theoretical pattern, or that natural tracking pattern which the axles would assume if influenced by natural steering forces only, by approximately 10%, and the front axle will over-steer approximately 3 /2%. To accomplish this, the arm 244 is lengthened somewhat, or the arm 242 may be shortened somewhat. Again assuming the distance between axles 16 and 18 to be 49 inches and the distance between axles 18 and 20 to be 109 inches, in the present instance the ratio of the lengths of the arms 244 and 242 is somewhat greater than 49 divided by 109, preferably enough greater so that the rear axle under-steers about 10% (that is, it assumes 10% smaller angle than it would in natural steering pattern), and the front axle over-steers about 3 /2% (that is, it assumes 3 /2% larger angle than it would in natural steering pattern).

Referring again to FIGURE 15, the lines 270 and 272 are extensions of the axles 16 and 20 illustrating the deviation of these axles from a natural steering pattern, as constrained by the stabilizer, when the towing vehicle is pulling the trailer at an angle which is normal to the line 210 in the drawing. Hence the projections of the steerable axles pass to the rear of the theoretical center 216, because of th action of the stabilizer herein described.

The lines 273 are like line 210 but are drawn at right angles to the towing vehicle in other angularly related positions with respect to the trailer.

A tandem axle vehicle having stiff axles has a maximum of directional (dead ahead) stability. However, side thrusts on the tires and wheels will rise in a constantly increasing ratio relative to the angle at the fifth wheel where tractive forces are applied. Hence there is a great deal of wear on the tires of a stiff axle vehicle, and Wear will be accelerated because of the fight between the axles. The present stabilizer reduces to a minimum tire wear on all axles not only in comparison to a stiff axle vehicle but also in comparison with a pivoted axle vehicle in which the stabilizer causes the axles to follow the natural tracking pattern exactly. Moreover, because the rearmost axle under-steers the theoretically perfect pat tern, it will trail properly without hunting or fishtailmg.

Referring again to FIGURE 17, the aspirating valves are connected to the reservoir by by-pass lines 280 through manual valves 282. Normally these valves are closed, but may be opened so that oil between both parts of the stabilizer system and reservoir can flow freely. By moving the vehicle slowly forward a few feet while these valves are open, the wheels are free to align themselves and the volumetric balance of the hydraulic system can be restored after whichthe shut-off valves may be closed. A normally open manual shut-off valve 284 is also provided in the conduit 260.

A second valve 286 is provided in line 260. Normally this valve is urged to open position by the spring 288 so that the stabilizer system is operative. Upon closing of this valve, the transfer of. hydraulic fluid between the cylinders 230 and 232 of the stabilizer system is blocked and accordingly the axles are locked. The valve 286 is shifted to open position by air above the level of oil in the reservoir. This air is under a pressure, for example about psi, and may be in communication with the air reservoir of the trailer brake system through line 290. A normally open manual shut-off valve 292 is provided in this line, and a check valve 294 is also provided permitting flow of air in a direction toward the reservoir only. The air in the reservoir communicates with the valve 286 to shift it to its closed position through a line 296 controlled by a normally closed valve 298. Valve 298 is a solenoid type valve which is operated whenever its solenoid is energized to shift from its normally closed position to open position.

The solenoid is energized through a circuit .300. There is shown in FIGURE 17 the normal vehicle battery 302 and the usual stoplight 304 which is operated Whenever the brakes are operated. The stoplight switch 306 may be directly connected with the brake pedal or with the air supply associated with the brake pedal. In any event, whenever the brakes are operated sufficiently to close switch 306 and energize stoplight 304, a circuit is completed to the solenoid of valve 298 causing it to open and admit pressure of air from the reservoir to shift valve 286 to closed position, thereby locking the axles. Accordingly, whenever the brakes are applied the steerable axles are locked against turning to prevent unstable steering reactions which might be caused by poor road surface conditions (such as slick or icy spots, etc.). Such a condition is possible, although not likely under normal conditions.

The circuit 300 is also adapted to be closed by a transmission switch 308. This switch is normally open, but is designed to be closed whenever the transmission is shifted into reverse. Accordingly, when the transmission is shifted to reverse for backing up the axles are locked.

FlGURE 16 shows a two-axle trailer 10' which has steerable axles 16' and 20, like the steerable axles 16 and 20 in the embodiment first described. Line 316 is drawn at right angles to the center line of a towing vehicle making a turn. Line 318 is drawn at right angles to the longitudinal center line of the trailer frame midway between the steerable axles, and 320 is the intersection between lines 316 and 318. Lines 322 and 324 are extensions of axles 16' and 18' and would intersect point 320 if such axles assumed a natural tracking pattern; However, interconnected by the stabilizer of this invention described in the foregoing, the front axle 16' oversteers and the rear axle 2t) understeers so that line 322 passes through point 326 and line 324 passes through point 328 on line 318.

amounts in opposite directions to assume the natural tracking pattern in response to steering forces alone, and if it were desired to have the axles actually follow such a pattern, the arms, similar to arms 242 and 244 of the three-axle trailer, would be equal in length since the cylinders are identical and the center of suspension or support lies on line 318. However, since it is desired that the rear axle understeer and the front axle oversteer, the arm connecting the rear axle to the rod of one cylinder would be longer than the rod connecting the front axle to the rod of the other cylinder.

What we claim as our invention is:

1.. A vehicle having a frame and equipped with brakes to reduce the speed of the vehicle when the vehicle is in motion, means for supporting the frame including an axle extending transversely of the frame, means pivotally connecting the axle to the frame for turning movement relative to the frame about a substantially vertical axis, means for locking said axle against turning movement about said axis and for positively holding said axle locked in whatever position it happens to be disposed when said locking means is operated, and means responsive to the actuation of the vehicle brakes for operating said locking means.

2. A vehicle having a frame, means for supporting the frame including a pair of axles extending transversely of the frame and spaced from each other lengthwise of the frame, means respectively pivotally supporting the axles on the frame for turning movement relative to the frame about substantially vertical axes, and a hydraulic stabilizer system interconnecting said axles to correlate the turning movements thereof, said stabilizer system including a pair of cylinders supported on said frame having pistons respectively slidably supported therein, fluid conduits respectively connecting the cylinders at opposite sides of the pistons, whereby sliding movement ofone piston in its cylinder imparts a sliding movement to the other piston in the opposite sense in its cylinder by the displacement of hydraulic fluid, and means operatively interconnecting the pistons of said cylinders and the respective axles to cause said axles to turn in opposite directions to positions such that the imaginary extensions of said axles have portions immediately adjacent the center of turn which pass behind the center of the turn, with reference to the direction of forward movement of the vehicle, so that the forwardmost axle of said pair of axles oversteers and the rearmost axle understeers the natural steering pattern, the center of the turn being that point where the imaginary extensions of the axles would intersect, when the vehicle is turned from a straight course of travel, if the axles assumed positions in exact conformity with the natural steering pattern.

3. A vehicle having a frame, means for supporting the frame including a pair of axles extending transversely of the frame and spaced from each other lengthwise of the frame, means respectively pivotally supporting the axles on the frame for turning movement relative to the frame about substantially vertical axes, said axes being spaced from the respective axles lengthwise of the frame to provide a caster effect enabling said axles to turn in opposite directions in response to turning of the frame from a straight course of travel, and a hydraulic stabilizer system interconnecting said axles to correlate the turning movements thereof, said stabilizer system including a pair of cylinders supported on said frame having pistons respectively slidably supported therein, fluid conduits respectively connecting the cylinders at opposite sides of the pistons, whereby sliding movement of one piston in its cylinder imparts a sliding movement to the other piston in the opposite sense in its cylinder by the displacement of hydraulic fluid, elongated members projecting radially Axles 16" and 20' tend naturally to turn in equal from'said axes and operatively connected to said axles to turn as a unit therewith, and means operatively connecting the outer ends of said members to the pistons of said cylinders so that turning of one axle in one direction causes a turning of the other axle in the opposite direction, said members being of such lengths as to cause said axles to turn oppositely to positions such that the imaginary extensions of said axles have portions immediately adjacent the center of turn which pass behind the center of the turn, with reference to the direction of forward movement of the vehicle, so that the forwardmost axle of said pair of axles oversteers and the rearmost axle understeers the natural steering pattern, the center of the turn being that point where the imaginary extensions of the axles would intersect, when the vehicle is turned from a straight course of travel, if the axles assumed, positions in exact conformity with the natural steering pattern the ratio of the length of the member for the rearmost axle to the length of the member for the forwardmost axle being somewhat greater than the ratio of the distance of the forwardmost axle from the center of suspension of the vehicle to the distance of the rearmost axle from the center of suspension, the center of suspension being located on the longitudinal center line of the vehicle where said longitudinal center line is intersected by a straight line drawn from the center of the turn normal to the longitudinal center line.

4. The vehicle defined in claim 3, wherein the aforesaid ratios are such that the forwardmost axle oversteers approximately 3 /2% (that is, it assumes a 3 /2% larger angle than if it tracked in conformity with the natural steering pattern), and the rearmost axle understeers approximately 10% (that is, it assumes a 10% smaller angle than if it tracked in conformity with the natural steering pattern).

5. A vehicle having brakes and a frame, means for sup porting the frame including a pair of axles extending transversely of the frame and spaced from each other lengthwise of the frame, means respectively pivotally supporting the axles on the frame for turning movement relative to the frame about substantially vertical axes, and a hydraulic stabilizer system interconnecting said axles to correlate the turning movements thereof, said stabilizer systems including a pair of cylinders supported on said frame having pistons respectively slidably supported therein, fluid conduits respectively connecting the cylinders at opposite sides of the pistons, whereby sliding movement of one piston in its cylinder imparts a sliding movement to the other piston in the cylinder by the displacement of hydraulic fluid, means operatively connecting the pistons of said cylinders and the respective axles, said interconnecting means being operative when the vehicle is turned from a straight course of travel to cause said axles to turn in opposite directions, means for locking said axles against turning movement and for positively holding said axles locked in Whatever position they happen to be disposed when said locking means is operated, said locking means including a shut-off valve in one of said conduits which is closed when said locking means is operated, and means responsive to the actuation of the vehicle brakes for operating said locking means.

6. In a vehicle comprising a supported assembly and a supporting assembly having tandemly arranged axles equipped with ground engaging wheels, at least one of said axles being mounted for turning movement relative to saidsupported assembly, suspension means for supporting the supported assembly on the supporting assembly comprising leaf springs on opposite sides of the vehicle disposed generally longitudinally of the vehicle, means connecting said springs to the opposite ends of said axles at points intermediate the ends of said springs, said connecting means for said turning axle including pivot means enabling pivotal movement between said turning axle and the springs to which it is connected about generally vertical axes, equalizer bars on opposite sides of the vehicle disposed generally longitudinally of the vehicle between said springs and pivoted intermediate their ends to said supported assembly for vertical swinging movement, and means coupling the ends of said springs to the ends of said equalizer bars, each said coupling means for the springs of said turning axle having parts respectively connected to a spring end and to an equalizer bar end, and a body pivoted to said respective parts for turning of the latter about axes which extend generally longitudinally with respect to the vehicle to enable the springs of said turning axle to have a lateral movement bodily with respect to the supported assembly without appreciable angular movement with respect to the supported assembly in response to turning movement of the turning axle.

7. The vehicle defined in claim 6, wherein said parts of each coupling means are pivoted to the ends of a spring and of an equalizer bar by horizontal pivots the axes ofwhich extend generally transversely of-the vehicle.

8. The vehicle defined in claim 7, wherein said leaf springs are of the single leaf type.

References Cited by the Examiner UNITED STATES PATENTS Chenoweth 280-1045 Fox 280-420 Merry 280-1045 Stover 280104.5 Stover 280--81 Ward 267-19 Stover 28081 Wilson et a1. 280-4045 Chalmers et al 280-4045 Hart 28091 Stump et al 28081 FOREIGN PATENTS France.

MILTON BUCHLER, Primary Examiner.

20 PHILIP ARNOLD, A. HARRY LEVY, Examiners. 

2. A VEHICLE HAVING A FRAME, MEANS FOR SUPPORTING THE FRAME INCLUDING A PAIR OF AXLES EXTENDING TRANSVERSELY OF THE FRAME AND SPACED FROM EACH OTHER LENGTHWISE OF THE FRAME, MEANS RESPECTIVELY PIVOTALLY SUPPORTING THE AXLES ON THE FRAME FOR TURBING MOVEMENT RELATIVE TO THE FRAME ABOUT SUBSTANTIALLY VERTICAL AXES, AND A HYDRAULIC STABILIZER SYSTEM INTERCONNECTING SAID AXLES TO CORRELATE THE TURNING MOVEMENTS THEREOF, SAID STABILIZER SYSTEM INCLUDING A PAIR OF CYLINDERS SUPPORTED ON SAID FRAME HAVING PISTONS RESPECTIVELY SLIDABLY SUPPORTED THEREIN, FLUID CONDUITS RESPECTIVELY CONNECTING THE CYLINDERS AT OPPOSITE SIDES OF THE PISTONS, WHEREBY SLIDING MOVEMENT OF ONE PISTON IN ITS CYLINDER IMPARTS A SLIDING MOVEMENT TO THE OTHER PISTON IN THE OPPOSITE SENSE IN ITS CYLINDER BY THE DISPLACEMENT OF HYDRAULIC FLUID, AND MEANS OPERATIVELY INTERCONNECTING THE PISTONS OF SAID CYLINDERS AND THE RESPECTIVE AXLES TO CAUSE SAID AXLES TO TURN IN OPPOSITE DIRECTIONS TO POSITIONS SUCH THAT THE IMAGINARY EXTENSIONS OF SAID AXLES HAVE PORTIONS IMMEDIATELY ADJACENT THE CENTER OF TURN WHICH PASS BEHIND THE CENTER OF THE TURN, WITH REFERENCE TO THE DIRECTION OF FORWARD MOVEMENT OF THE VEHICLE, SO THAT THE FORWARDMOST AXLE OF SAID PAIR OF AXLES OVERSTEERS PATTERN, THE MOST AXLE UNDERSTEERS THE NATURAL STEERING PATTERN, THE CENTER OF THE TURN BEING THAT POINT WHERE THE IMAGINARY EXTENSIONS OF THE AXLES WOULD INTERSECT, WHEN THE VEHICLE IS TURNED FROM A STRAIGHT COURSE OF TRAVEL, IF THE AXLES ASSUMED POSITION IN EXACT CONFORMITY WITH THE NATURAL STEERING PATTERN. 